The present invention relates to a fuel injection control device and method for an internal combustion engine.
Japanese Laid-Open Patent Publication No. 2016-8569 discloses a fuel injection control device employed in an internal combustion engine configured to execute a full-lift injection, in which the needle valve of the direct injector that injects fuel is fully opened, and a partial-lift injection (an intermediate-lift injection), in which the needle valve of the direct injector is not fully opened. This fuel injection control device divides the amount of fuel corresponding to the injection amount required for a single combustion into portions corresponding to multiple fuel injections, and causes the direct injector to inject the fuel in the multiple times. In addition, the fuel injection control device causes the direct injector to execute the partial-lift injection as the final fuel injection of the multiple fuel injections.
In the above-described technique, the final fuel injection of the multiple fuel injections is executed for the purpose of stratifying fuel to form, in the vicinity of the spark plug, a fuel stratum that is richer than the other regions. For this reason, if the injection amount at the final fuel injection varies, the combustion state tends to vary for each cylinder and each combustion. Therefore, it is desired that the final fuel injection of multiple fuel injections be executed with an accurate injection amount with small variation.
Depending on the method of calculating the injection amount by the fuel injection control device, a small injection amount may be calculated as the injection amount at the final fuel injection of the above-described multiple fuel injections. Since the position of the needle valve is unstable in the fuel injection of the partial-lift injection as compared with the case of the full-lift injection, the smaller the injection amount, the greater the variation in the injection amount becomes. Therefore, if an excessively small injection amount is set as the execution value of the injection amount at the final fuel injection, there may be variation in the combustion state for each cylinder and each combustion.